We have developed a program, RigiMol, which applies a geometric analysis and clustering algorithm to identify rigid domains and rigid body motions in ensembles of protein structures. The proram has the capability of generating interpolated molecular structures which can be converted into movies using software such as UCSF MidasPlus. We are using the Computer Graphics Laboratory facilities to generate a number of such movies which will improve our understanding of how protein structures behave. The focus of this work is how protein structures and surfaces adapt when they form complexes with small molecules and other proteins. We are studying the interactions between IgG-Fc and a number of IgG-Fc binding proteins and peptides. With the newly developed RigiMol software and CGL resources, it is now possible to conduct a more thorough analysis of existing IgG-Fc complex structures.